Why so scarce in our coastal state? CT's sheltered coastline and lack of open ocean (thanks to Long Island) are just not very attractive to these terns. Arctic Tern breeds to our north and winters well to our south, but they generally head straight out to sea for migration. Long Island Sound just doesn't cut it.
There are a few mechanisms by which this species might be found in CT:
1) Tropical Storm - A late-summer cyclone could conceivably dump any pelagic species into LI Sound, and Arctic Tern can be (and already has been) seen in CT following one of these storms.
2) Spring migration - This species is occasionally seen in our region during mid-late May, often during an out-of-season nor'easter or other inclement weather.
And, what I really want to talk about:
3) Early-summer immatures
While adult Arctic Terns spend their summers breeding to our north, one-year-old birds are not yet of breeding age. These individuals may spend their first summer well south of the species' breeding range. These young birds look a lot like adults in non-breeding plumage, sporting incomplete black caps, black bills, and blackish legs.
My blurry photo of a first-summer Arctic Tern (right) next to an adult Common Tern, taken at South Beach, Cape Cod, MA on 5 Jul 2005.
These individuals occur regularly on Long Island and Cape Cod, usually among flocks of Common Terns. They peak from mid-June to early-July. For instance, in 2008 there were 8 Arctic Terns seen on Long Island during this time period (mostly immatures).
I've done some thinking about where to find such birds in CT. I think your best shot would be a Common Tern roost as far east as possible. The site that always comes to mind for me is Griswold Pt in Old Lyme at low tide, where Common (and Roseate) Terns often roost during the summer months. Milford and Sandy Pts also come to mind, but both sites are currently tern-less.
Can anybody else think of a spot that has roosting Common Tern flocks, particularly in the eastern part of the state?
Checking such a site regularly over the next 6 weeks could yield one of these beauties. Keep an eye out for first-summer Common Terns as well, which occur in small numbers at this time of year. The separation of Arctic from Common Tern relies more heavily on structure than on plumage details (although plumage, especially wing pattern, is important), so if you're lucky enough to see some one-year-old Common Terns this month, take the extra time to study them closely.